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Author:Tamminen, Teemu
Title:Final bleaching of kraft pulp: The optimization of the first chlorine dioxide stage (D1)
Sulfaatiselluloosan loppuvalkaisu: Ensimmäisen klooridioksidivaiheen (D1) viipymäajan optimoimti
Publication type:Master's thesis
Publication year:2010
Pages:91 + [18]      Language:   eng
Department/School:Puunjalostustekniikan laitos
Main subject:Selluloosatekniikka   (Puu-23)
Supervisor:Sixta, Herbert
Instructor:Vehmaa, Janne
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  2355   | Archive
Keywords:ECF
chlorine dioxide
final bleaching
D1 stage
retention time
klooridioksidi
loppuvalkaisu
D1-vaihe
viipymäaika
Abstract (eng): The final bleaching stages of a typical fiber line, producing papermaking pulp, have the longest retention times in the bleaching sequence.
Thus, they require large towers which increase the investment costs.
The knowledge and the studies about the effect of retention time on the efficiency of D1 stage derive from the 1970s and 1980s.
The bleaching technology has developed in many fronts after those days, for example, in mixing.
The aim of this thesis was to study the effects of the retention time on the performance of a modern D1 stage.

The literature part reviews the process conditions and the technology of chlorine dioxide bleaching.
Attention is directed on the formation and reactions of different chlorine species in chlorine dioxide bleaching.
The incoming chromophores, their reactions, and changes in a D1 stage are also discussed.

The test series in the experimental part were first performed in a laboratory medium consistency mixer.
The most important variable was the retention time, but also the pH and temperature were altered.
The laboratory experiments were followed by a mill trial, in which pulp samples were extracted after the chemical mixing of the D1 stage and bleached in polyethylene bags with varying retention times.

In all the test series the chlorine dioxide (ClO2) consumption was rapid.
The longest retention time, which was required to virtually consume the charged ClO2, was 60 minutes.
Maximum brightness values were attained with the same retention times which had virtually consumed the dosed ClO2.
After the active chemicals were consumed the brightness began to decline.
The disadvantage of the shorter retention times was that the brightness reversion was declining with longer retention times.
The reasons behind the declining brightness and brightness reversion values could not be confirmed in this thesis.

The results from the experimental part clearly indicate that there is potential to shorten the retention times of D1 stages.
According to the results of the experimental part the optimum retention time in a D1 stage consumes the charged ClO2 but the reaction time is not extended further.
Abstract (fin): Sellutehtaiden kuitulinjoilla loppuvalkaisuvaiheiden viipymäajat ovat tyypillisesti pitkiä.
Pitkät viipymäajat vaativat suuret valkaisutornit, jotka lisäävät investointikustannuksia.
Perustutkimus viipymäajan vaikutuksesta D1 -vaiheeseen on peräisin 1970- ja 1980-luvuilta, jonka jälkeen valkaisuteknologia on kehittynyt monilla osa-alueilla esimerkiksi sekoituksessa.
Diplomityön tavoitteena oli tutkia viipymäajan vaikutusta nykyaikaisen D1 -vaiheen suorituskykyyn.

Työn kirjallisuusosassa kuvataan prosessiolosuhteita ja teknologiaa klooridioksidivalkaisussa.
Huomiota kiinnitetään eri klooriyhdisteiden muodostumiseen ja reaktioihin klooridioksidivaiheessa.
Lisäksi kirjallisuusosassa tutustutaan D1 -vaiheeseen tuleviin kromoforiyhdisteisiin sekä niiden reaktioihin ja muutoksiin D1 -vaiheessa.

Kokeellisen osan kaksi ensimmäistä koesarjaa joissa simuloitiin D1 -vaihetta, suoritettiin laboratorion keskisakeusmikserissä.
Tärkeimpänä muuttujana oli viipymäaika, mutta myös pH:ta ja lämpötilaa muutettiin.
Laboratoriokokeiden jälkeen suoritettiin kaksi tehdaskoesarjaa.
Tehdaskoesarjoissa näytteenotto suoritettiin D1 -vaiheen kemikaalisekoituksen jälkeen ja valkaisu polyeteenipusseissa tehtaan laboratoriossa.

Klooridioksidin kuluminen oli nopeaa jokaisessa koesarjassa.
Pisin viipymäaika, joka tarvittiin kuluttamaan klooridioksidiannos loppuun, oli 60 minuuttia.
Vaaleusmaksimit saavutettiin viipymäajoilla, joilla klooridioksidiannos oli juuri kulunut loppuun.
Massojen jälkikellertyminen väheni viipymäaikojen kasvaessa.
Syy vaaleuden ja jälkikellertymisen laskuun viipymäajan pidentyessä jäi epäselväksi.

Diplomityön tulosten perusteella D1 -vaiheiden viivettä on yleisesti mahdollista lyhentää nykyisestä 2 - 4 tunnista.
Työn tulosten perusteella optimaalinen viipymäaika D1 -vaiheessa kuluttaa klooridioksidin loppuun.
Aktiivisten valkaisukemikaalien loputtua massan vaaleus alkaa laskea jos viipymäaikaa jatketaan.
ED:2010-06-02
INSSI record number: 39714
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